BEMBRiDGE BEDS. 



159 



Fig. 51. 

 Bulimus elUpticus, Sow. 



section. Among the grassy slopes beneath the gravels that crown 

 the summit of the hill, white and yellowish sandy marls appear 

 here and there in the broken ground, occasionally varied by con- 

 taining hard white C(mipact limestone nodules that break with 

 a sharp-edged, splintering fracture. A little to the north of the 

 summit these beds, dipping northward, l)ecome rather more de- 

 veloped, passing into concretionary and travertinous limestones. 

 The bo^iics regarded by Mr. Edwards as turtle's eggs occur 

 among them in regular lines. The fossils found in the con- 

 cretions are almost invariably terrestrial, and consist of Helix 

 D'Urhani, H. omphalus, H. occlusa, H. headonensisl Bulimus 

 elUpticus, Pupa pcvdentata, and Cyclotus cinctus. 



Bulimus elUpticus (Fig. 51), Helix 

 glohosa (Fig. 52), Planorbis discus 

 (Fig. 53), &c., have been obtained 

 from these beds b}- the fossil collectors 

 of the Geological Survey, mostly in 

 the condition of casts, but the shell is 

 sometimes replaced b}^ calc-spar, which 

 also occurs in a crystalline form lining 

 and filling small cavities in the stone. 

 As a general rule, the Bembridge 

 Limestone may be distinguished from 

 the thick Upper Headon Limestones, 

 as well as from those in the lower 

 groups, by its greater whiteness and 

 its peculiar brecciated or tufaceous 

 character, as well as by the fossils 

 either being casts, or having their 

 shells replaced by calc-spar. The 

 Headon Limestones, on the contrary, 

 are of a somewhat darker cream- 

 colour, more earthy and soft in com- 

 position, and have the shells of the 

 LimncB(B and other fossils preserved. 



The total thickness of this lime- 

 stone at Headon Hill is from fifteen 

 to sixteen feet. It is surmounted by a 

 greenish-grey marl with Cyrena obovata 

 having both valves in contact, which 

 passes upwards into a soft, unctuous, 

 earthy limestone, containing Planorbis 

 and a large LimncBu, which again 

 merges upward into very tenacious 

 grey clay, weathering brown and 

 black, and carbonaceous on the top. 

 In thickness these deposits are variable, 

 even within short distances, the limestone being sometimes as much 

 as three feet, while the clay resting upon it varies from three to four- 

 teen inches. In one place, however, where the three deposits formed 



Fig. 52. 

 Helix globosa. Sow. 



